Stacked land grid array package

ABSTRACT

A spring plate may be provided between a bolster plate and a board in order to mount components on the opposite side of the board. In some embodiments, the spring plate may provide additional stack tolerance and forceful bias to hold the stack tightly together.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/844,765, filed on May 13, 2004.

BACKGROUND

This invention relates generally to packaging integrated circuits.

Integrated circuits, such as microprocessors, may be packaged in variousconfigurations. One such configuration is called a land grid arraypackage. With land grid array packaging, integrated circuit die may becoupled to circuit boards through sockets that electrically andmechanically couple the integrated circuit die to the circuit board. Insome cases, the connection may be via socket spring fingers whichcontact lands on the integrated circuit packages to make a land gridarray connection system.

Often, a number of components may be connected together to form a stack.In one example a voltage regulator module board may be assembled on amotherboard through a land grid array connector. The voltage regulatormodule and motherboard are clamped together between a bolster plateunder the motherboard. A heat sink may be positioned on top of thevoltage regulator module board. Pairs of standoffs on the bolster plateare used to control the space in between the bolster plate and the heatsink.

Due to the dimensional tolerances of the mechanical parts, the distancebetween the bolster plate and the heat sink varies on individualassembly. Part of this stack tolerance can be absorbed by theflexibility of the land grid array springs. However, the bending rangeof land grid array springs is limited and cannot absorb the entire stacktolerance.

In the meantime, a certain level of pressure is required to press theland grid array onto the land pads on the motherboard to meet therequirement of good electrical design.

Thus, there is a need for better ways to connect integrated circuits toboards in the form of stacks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged, cross-sectional view through one embodiment ofthe present invention;

FIG. 2 is a cross-sectional view taken generally along the line 2-2 inFIG. 1;

FIG. 3 is a perspective view of a spring plate in accordance with oneembodiment of the present invention;

FIG. 4 is a perspective view of a spring plate in accordance withanother embodiment of the present invention; and

FIG. 5 is a system schematic according to one embodiment of the presentinvention.

DETAILED DESCRIPTION

Referring to FIG. 1, a land grid array package stack 10 may include avoltage regulator module heat sink 12 mounted on a voltage regulatormodule board 14. Under the board 14 may be a voltage regulator modulesocket or connector 16. The connector 16 may be positioned over amotherboard 18 which, in turn, is positioned over an insulator 20 in oneembodiment. The board 14, connector 16, board 18, and insulator 20 maybe mounted on a set of standoffs 30 which allow relative verticalmovement of the stack 10 while controlling the side to side or lateralmovement thereof. A screw 50, in turn, is connected through thestandoffs 30 to a bolster plate 22 on the bottom of the stack 10 to holdthe stack 10 together. Between the bolster plate 22 and the board 18 ispositioned a spring plate 24.

In some embodiments, the spring plate 24 provides the required pressingload on the back of the board 18 and thereafter on the land grid arrayconnector 16, while absorbing the stack tolerance. As mentioned above,due to the dimensional tolerance of the mechanical parts, the distancebetween the bolster plate 22 and the heat sink 12 may vary on individualassembly. While part of this tolerance can be absorbed by theflexibility of the land grid array connector springs, the entiretolerance cannot be so absorbed. Thus, the spring plate 24 may functionto absorb that tolerance. In some embodiments, the spring plate cansupply a recovery force while reducing or even minimizing the tilting oruneven contact of the land grid array connector 16 on the board 18.

To this end, the spring plate 24 may include two or more pairs ofindependent spring legs 32 as shown in FIG. 2. The spring plate 24 maybe formed of stamped metal in one embodiment of the present invention.For example, the spring plate 24 may be made of BeCu alloy which has alower Young's modulus and a higher yield strength than steel.

A set of four spring legs 32 may be positioned on the center bar 34 ofthe spring plate 24 in one embodiment. The spring legs 32 may bepartially cut out of the rest of the plate 24 and may be bent upwardly,towards the board 18, as the spring legs extend away from the center bar34. The free ends 40 of the spring legs 32 may be bent over to preventgouging of the mating surfaces. The span in the spring legs 32 may beless than half of the plate 24 width in some embodiments.

Clips 26 and 28 may be provided to ease assembly. For example, in oneembodiment, the clips 28 extend downwardly from one half of the plate 24while the clips 26 extend upwardly from the other half of the plate 24,as shown in FIG. 3. In other words, the clips 26 may engage the sides ofthe board 18 while the clips 28 engage the sides of the bolster plate 22in one embodiment. The center bar 34 may include U-shaped openings 42 toreceive the standoffs 30 in one embodiment of the present invention.

In some embodiments of the present invention, the spring plate 24provides a low profile spring to absorb the stack tolerance whilemaintaining the desired pressure force in a limited space.

The spring legs 32 may be made by cutting and forming sheet metal in oneembodiment of the present invention. For example, stamping may beutilized for this purpose.

The free ends 40 of the spring legs 32 are closer to the edges of theplate 24, while the lower ends sit closer to the plate center bar 34.The free ends 40 contact the object being supported. Larger spacing maybe achieved between the free ends 40 due to this configuration which cansupply a recovery force to reduce or minimize the tilting of theconnector 16 relative to the board 18.

The height of the free ends 40 depends on the application and may beminimized to maintain a low profile in some embodiments. The free stateheight can be no larger than 10 percent of the plate 24 width in oneembodiment of the present invention. The preload height can be less thanone millimeter in one embodiment of the present invention. The use ofthe rounded free ends 40 may avoid any concentrated contact andscratching of other components in some embodiments.

The spring plate 24 uses a closed design as shown in FIG. 3 with turnedfree ends 40. The arms 32 may be straight as shown in FIG. 3. The plate24 may provide better structural integrity in some embodiments.

Alternatively, an opened design may be utilized in the plate 24 a asshown in FIG. 4. In the opened design, there are no turned over freeends 40. In addition, the arms 32 may be curved. The opened design mayprovide for more flexibility in some embodiments.

In one embodiment of the present invention, the length of each springleg 32 may be 16 millimeters and the span of the spring leg may be 4millimeters. The free state height of the raised end 40 may be 1.5millimeters with a plate thickness of 0.4 millimeters in such anembodiment. Such a structure can absorb a working stack tolerance rangeof about 0.6 millimeters, while maintaining the total pressing force atgreater than 40 pounds.

Referring to FIG. 5, in accordance with one embodiment of the presentinvention, a system 50 may be implemented by a motherboard 18 and avoltage regulator module board 14. The motherboard 18 may include aprocessor 52, a system memory 56, and a bus 54. The connector 16 couplesthe voltage regulator module 58 to the bus 54. While FIG. 5 shows onesystem implementation of the present invention, those skilled in the artwill appreciate that the present invention is in no way limited to anyparticular system implementation.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

1. A spring plate assembly comprising: a sheet of resilient material; aplurality of spring arms formed to extend from said sheet of material inthe same direction; and sets of opposed clips extending from saidmaterial in opposite directions.
 2. The assembly of claim 1 wherein saidspring arms are curved.
 3. The assembly of claim 1 wherein said springarms are straight.
 4. The assembly of claim 3 wherein said spring armshave offset ends.
 5. The assembly of claim 1 wherein said sheet has apair of opposed ends and each end has a pair of oppositely extendingclips.
 6. The assembly of claim 5 including slots extending into saidopposed ends of said sheet.